This invention relates generally to casting and, more specifically, to casting metal sinkers wherein the liquid metal expands upon solidification causing the cast article to tenaciously adhere to the mold.
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Traditional lead sinkers have been used as weights for fishing lines. Because of environmental concerns manufactures have proceeded to make sinkers from other metals or metal alloys. One of the metals ideally suitable for use in sinkers is bismuth since it has a high specific gravity. Unfortunately, bismuth has a peculiar solidification characteristic that makes it difficult and costly to form sinkers therefrom. As bismuth cools it expands rather than shrinks, consequently, upon cooling the bismuth article forms an interference fit with the mold making it extremely difficult to remove. Coupled with the fact that bismuth is a brittle type metal one can easily shatter a bismuth cast article by attempting to drive the cast bismuth article from a mold. The present invention provides a method and mold that allows one to cast sinkers from metals such as bismuth, bismuth alloys or other metals that expand during solidification while at the same time overcoming the peculiar solidification characteristics which normally produces an interference fit between the cast article and the sidewalls of the mold cavity that prevent freeing of the article without damaging the cast article.
Briefly, the present invention comprises an expandable mold for use with metals that expand during solidification with the expandable mold having sidewalls that are forcibly laterally separated to thereby expand the mold cavity sufficiently so as to free at least one portion of the cast article from an interference fit with a first portion of the mold to thereby enable removable of the cast article from an interference fit with a f further portion of the mold without fracture of the cast article. A further feature of the invention is allowing the metals to enter the solidification phase where expansion occurs one can produces a smooth finish on the cast article.